Cellulose-based filter aids have been known for a long time (xe2x80x9cUllmann""s Encyclopedia of Industrial Chemistry, 3rd edition (1951), first volume, page 492, key word xe2x80x9cfelted layersxe2x80x9d and page 493, key word xe2x80x9cfilter aidsxe2x80x9d). Cellulose is produced in a multi-step chemical process, in which all sensorially active materials are removed from the raw material.
Hence filter aids made of pure cellulose are used wherever the sensorial neutrality of the used filter aid is of great significance. Examples of cellulosic filter aids are EFC (low extract cellulose), fine powder cellulose, fine fibrillated cellulose, cationized powder cellulose, fine MCC (microcrystalline cellulose).
In contrast, filter aids made of untreated woodpulp are produced by mechanical comminution, thus only by physical treatment, and can, thus, release extractives (color, odor, flavor) during filtration. Therefore, the use of natural wood fiber-based filters is usually limited to industrial filtrations, where relatively little demand is placed on the sensory analysis. Not only for filtration in the food and luxury food sector, e.g. for sugar solutions (glucose, dextrose, fructose), molasses, dye solutions, fats and oils and the like, but also for many industrial applications, they may be considered only if either the subsequent refining or the complete removal of undesired components (activated charcoal, ion exchanger, etc.) or if the extractives substances cannot have a negative impact on the process (lamination or neutralization due to dyes and odorous substances intrinsic to the process).
The difficult sector of beverage filtration demands, on the one hand, complete sensorial neutrality of the used filter aid; on the other hand, the number of alternatively used filter aids is limited for economic reasons, since the maximum expense for the filter aid is fixed by the price of the mineral filter aids dominating this market.
Usually beverages are filtered in two steps. The first step usually involves mechanical separation methods (e.g. centrifuges) or a coarse filtration, during which operation the liquid usually passes through a precoat layer of a filter aid. This step is frequently followed by a fine filtration operation.
The standard filter aid for filtering by means of a precoated filter in the beverage, especially beer, sector, is kieselguhr. A high percentage of the world beer production is clarified by kieselguhr filtration. Currently it exceeds more than 1.1 billion hl of beer.
It is estimated that the total demand for filter aids worldwide is approximately 1 million tons per year, where inorganic materials, such as kieselguhr, perlite or bentonite, constitute by far the largest share of this amount. Of this total amount about 250,000 tons to 300,000 tons per year are consumed worldwide by the beverage industry, largely by breweries, but also by producers of wine and fruit juices.
To date the number of filter aids, which are based on organic, sustainable raw materials (cellulose, woodpulp, etc.), has been only approx. 60,000 tons per year, even though their use offers a plurality of advantages over inorganic filter aids.
The specific consumption can be up to 70% lower as a result of the low wet cake density (compared to mineral filter aids). At the same time the fibrous structure, the fissured surface and the high porosity often result in a higher flow rate and longer filter life. The structure of plant and cellulose fibers allows the filter to respond elastically to pressure thrusts. They bridge minor defects in the filter cloth; their internal interconnectiveness makes subsequent cleaning of the filter cake easier. Furthermore, the use of organic filter aids presents neither a health risk nor harmful effects for the environment and nature. Pumps and conveying elements of the filtration systems are protected as much as possible owing to the non-abrasive property. Finally the spent filter cakes can be easily disposed, for example, through land management, composting or animal fodder.
Of course, organic filter aids are to some extent many times more expensive than kieselguhr or they exhibit filtration properties that do not completely match those of kieselguhr.
For this reason organic filter aids have not been able to prevail to date against kieselguhr or are used in any case together with kieselguhr (J. Speckner""s report xe2x80x9cCellulose as Filter Aidsxe2x80x9d in the journal xe2x80x9cBrauweltxe2x80x9d, vol. 124 (1984), issue 46, pages 2058 to 2066, in particular page 2062, left column at the top).
However, using kieselguhr has become increasingly a problem. It arises predominately from the fact that the users have become increasingly more critical in their attitude toward kieselguhr, since diverse studies have suggested in the interim that specific types of kieselguhr pose lung problems.
Strict regulations, which are being asserted and observed more and more in Germany, apply to the handling of kieselguhr.
Another factor is that the disposal of kieselguhr is becoming increasingly more critical in industrial countries. In many places kieselguhr-containing filter residues must be brought to the landfill, a condition that results in a high cost. In contrast, organic filter aids can be tied in again into the natural raw material cycle through composting or animal fodder, a condition that relieves the landfill and provides closed disposal plans.
If contaminated filter cakes from chemical applications have to be fed to thermal utilization, the high ash content and low intrinsic fuel values of mineral filter aids pose a problem.
The result of these urgent problems has been to investigate the possibility of replacing mineral filter aids, especially kieselguhr, when filtering beverages and similar liquids. For a long time, these investigations have paid special attention to using cellulose as a filter aid. Of course, cellulose has been known for a long time as a filter aid. However, for the present invention the issue is using cellulose in the final step of beer filtration which is supposed to largely remove germs and correspondingly stabilize the product (see J. Speckner xe2x80x9cCellulose as a Filter Aidxe2x80x9d, Brauwelt, vol. 124 (1984), issue 46, pages 2058 to 2066; K. Wackerbauer and R. Gaub xe2x80x9cP and S Filtration in Practical Trialsxe2x80x9d, Brauwelt (1989), issue 35, pages 1680-1689).
As a sustainable natural material, cellulose is relatively easy to obtain and passes effortlessly again into the natural cycle without leaving behind any harmful effects.
Therefore, there already exist attempts to provide a filter material that is made exclusively of cellulose and cellulose derivatives, and that exhibits no components that are harmful to human health or the environment and whose separation efficiency is at least just as high as that of the prior art asbestos-free deep bed filter layers, and that exhibits very few extractable components (DE 43 09 845 C2).
However, the prior art filter aids exhibit a cellulose acetate fiber content ranging up to 50 percent by weight of the total quantity. As a structural component that provides the internal interconnectivity, the cellulose acetate fibers are to be present in a quantity of up to 50% of the total weight of the filter aid. Both microcrystalline and microfine cellulose are distributed homogeneously and embedded in the structure. They can move in the structure and thus have a homogenizing effect on the filter layer.
The requisite cellulose acetate for the filter aid, according to the DE 43 09 845 C2, constitutes a plastic material, which exhibits no natural organic components and is not degradable in the same manner as the cellulose content of this filter aid.